ABSTRACT
The present study was to identify better/cheaper sources of lipase with suitable kinetic properties for biotechnological applications. Lipase was purified from two fungal isolates (Aspergilus nidulans and Aspergillus niger) and partially characterized based on effects of pH, temperature, and metal ions on lipase activity. Screening the two fungal isolates, white zones of precipitation appeared round the isolates on Tween 80: Agar plates, indicating their capability for producing extracellular lipase. Highest lipase production by Aspergilus nidulans (A. nidulans) was achieved in three days (72 h) at pH 5 whereas that of Aspergilus niger (A. niger) was achieved in 5 days (120 h) at pH 6. The suitable ammonium sulphate saturation for precipitation of the lipases was found to be 70%, with A. nidulans lipase showing a weak/secondary peak at 30% salt concentration. Results of pH studies revealed that lipase from A. nidulans had optimal pH of 7 with activity of 221.05 µmol/min, while lipasefrom Aspergilus niger had a pH optimum of 6 with activity of 421.05 µmol/min. At pH optima of the two lipases, lipase activity increased concurrently with increase in temperature up to their optimal values: 40°C (452.6 µmol/min) for A. nidulans lipase and 50°C (821.1 µmol/min) for A. niger lipase. Beyond these values, activity dropped in each case. Kinetic parameters, Vmax and KM, were calculated from the double reciprocal plots for the two lipase sources. Lipase from A. nidulans, had a higher Vmax (769.23 μmole/min) than the lipase from A. niger (Vmax = 714.29 μmole/min) and lager Km value (17.54 mg/ml) compared to that of the lipase from A. niger (Km = 9.71 mg/ml).
